EUV Laser Prepulse Energy Control via Off-Droplet Decoupling
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Solution Overview
Problem
In EUV light source systems, the energy of prepulses (PP energy) tends to drift or jump, leading to instability in the EUV power output, resulting in a loss of 1% to 4% EUV power due to coupling between the EUV dose control loop and the PP energy control loop.
Innovation Solution
Measuring and controlling off-droplet PP energy to set a pulse energy setpoint, decoupling the EUV dose control loop from the PP energy control loop, allowing open-loop control of prepulse energy during on-droplet periods, thereby avoiding negative side effects and maintaining EUV power stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the EUV dose control loop and PP energy control loop are coupled, then the system can control both EUV dose and prepulse energy, but the EUV power stability deteriorates due to interference between the two control loops
Solution Approach 1:
The patent divides the coupled control system into two independent control loops: an EUV dose control loop and a PP energy control loop. By segmenting the control functions, each loop can operate independently without interfering with the other, thus maintaining EUV power stability while preserving both control capabilities.
Solution Approach 2:
The patent extracts the PP energy control function from the EUV dose control loop, creating a separate dedicated control loop for PP energy. This extraction eliminates the negative interference that occurred when both controls were coupled, allowing stable operation of both functions simultaneously.
2Device complexity
If PP energy is not controlled, then the control system is simpler, but PP energy drifts and jumps causing EUV power loss
Solution Approach 1:
The patent implements a feedback control mechanism in the PP energy control loop that measures actual PP energy and adjusts it to maintain stability. This feedback system prevents PP energy drifts and jumps without requiring complex system architecture, achieving reliable PP energy control through straightforward measurement and adjustment.
3Stability of the object's composition
If on-droplet PP energy is measured and controlled, then PP energy stability improves, but the EUV dose control range is reduced due to loop coupling
Solution Approach 1:
The patent segments the control loops so that PP energy measurement and control occur in an off-droplet mode, separate from the on-droplet EUV dose control. This segmentation allows full PP energy stability during on-droplet periods while maintaining complete EUV dose adjustment range, as the two controls no longer interfere with each other.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively stabilizes the EUV power output by decoupling control loops, preventing energy fluctuations and maintaining the available dose adjustment range, thus enhancing the overall efficiency of EUV generation.
Implementation Method 1
a laser source of pulsed laser radiation, the laser source being configured to operate in an exposure mode in which the droplets of source material are irradiated by laser pulses
Implementation Method 2
irradiating a source material, for example, in the form of a droplet, stream, or cluster of source material, with an amplified light beam that can be referred to as a drive laser. For this process, the plasma is typically produced
Implementation Method 3
an energy controller configured to perform an energy measurement of the at least one off-droplet pulse during the nonexposure mode and to drive the pulse energy to a pulse energy setpoint based at least in part on the energy measurement
Data Source
AI summary
Disclosed is an apparatus and a method in which off-droplet measurements instead of on-droplet measurements of prepulse energy are used for pulse energy control. Prepulse energy is measured during an off-droplet nonexposure period and controlled to a prepulse energy setpoint. The prepulse energy can then be controlled open-loop to the prepulse energy setpoint during on-droplet periods. This effectively decouples the EUV dose control loop from the prepulse energy control loop and avoids negative side effects of coupling such loops, for example, loss of the part of the dose adjustment range available to the dose controller.